Mastocytosis is a disease of disordered mast cell proliferation. It affects all ages, both sexes, and all ethnic groups. In some cases, mastocytosis has an aggressive and ultimately fatal course. Thus, our efforts are directed to improving diagnosis and treatment; and to clarifying the etiology of this disease. A successful approach to treatment for aggressive disease remains elusive. However, in vitro studies demonstrate that IFN-gamma-1b does suppress human mast cell growth, where IFN-alpha-2b does not. Studies on c-kit and the relevance of activating mutations which we first identified (Asp816Val; Asp816Tyr) in mastocytosis patients are continuing. Data now indicates all patients with mastocytosis appear to have the point mutation at position 816 in some peripheral blood cells and in skin lesions. In contrast, pediatric patients with mastocytosis may demonstrate this mutation only in skin lesions; and in some children no mutation in c- kit can be identified. Molecular studies are consistent with the conclusion that the Asp816Val mutation is a somatic mutation and is not in germ line tissues. There is no consistent chromosomal abnormality in mastocytosis. However, cytogenic abnormalities are more frequent in aggressive disease and in those whose PBMC?s show the Asp816Val mutation. - Mastocytosis, mast cell, sequencing, interferon, stem cell factor, c-kit - Human Subjects